Paper is formed from a variety of different materials and to a variety of different specifications. For example, card stock is manufactured from fibers derived from the Kraft paper process, among others. These fibers are formed from wood, chemically broken down into fibers. They generally contain a large amount of pitch. The card stock itself is relatively thick and produced at slower speeds.
Newsprint is formed from varying amounts of recycled paper and mechanically separated wood derived fibers. Therefore the fiber characteristics are significantly different. Newsprint is thinner than card stock and produced at a much faster speed.
During the manufacture of paper, a web of paper fibers derived from wood sources and also from recycled paper sources is typically formed on the surface of a fabric mesh which is used to drain excess water from the web. The drained web of paper fibers is then introduced into a series of rolls, some of which are covered by continuous belts of fabric or felt. As the paper web is fed through the rolls and between the layers of felt, pressure is applied to the paper web which forces water from the web.
The paper web contacts the surface of some rolls directly. Pressure is applied in these instances to make the paper smooth. The surface of the roll may be rubber, steel, chrome steel, ceramic, minerals such as granite and various composite materials. Surface tension causes the paper web to adhere to the surface of the papermaking roll.
Because of the thinness of the formed paper as well as the speed at which the rollers operate, surface tension between the papermaking roll and the paper web presents a significant concern with newsprint and other thinner papers. Higher surface tensions will tend to force one to operate at slower speeds and can cause more frequent web breaks. This combines to decrease the speed at which the paper is produced and thereby increasing its overall expense. Also the deposition of various organic materials, both synthetic and naturally derived onto the surface of a papermaking roll causes excessive adhesion of the papermaking web to the roll surface. This deposition is a major factor in the development of poor sheet release especially in grades of papers using pulp from recycled sources or using pulp from resin containing woods.
The present invention is premised on the realization that surface tension between a papermaking roll and a paper web can be significantly reduced by continuously coating the surface of the papermaking roll with a liquid mixture including a cationic polymer, a non-ionic surfactant and an anionic surfactant. The amount of the anionic surfactant relative to the cationic polymer is such that the cationic polymer retains a substantial portion of its positive charge, generally 10%-50%.
More preferably the cationic polymer is a poly-diallyidimethyl ammonium chloride and the anionic surfactant is a carboxylated linear alcohol, although a wide variety of other polymers and surfactants can be employed.
This is particularly effective at reducing surface tension at high speed mills producing thinner finer paper products which generally operate at 2800 to 4100 ft./min.
The invention will be further appreciated in light of the following detailed description.
The present invention is a method of reducing surface tension between papermaking rolls and the web as it is being compressed and keeping the surface of a papermaking roll free of deleterious deposits. This is accomplished by applying the composition of the present invention directly to the papermaking rolls. The composition of the present invention comprises a cationic polymer in combination with a non-ionic surfactant and an anionic surfactant.
A wide of variety of cationic polymers can be used in the present invention. In general, these cationic polymers must be water soluble and are formed from cationic monomer units or both cationic and non-ionic monomer units. By the term catonic is meant that the monomer unit includes a group which either carries a positive charge or which has basic properties and can be protonated under mild acidic conditions.
Suitable polymers include cationic addition and condensation polymers. The polymer will generally be composed partially of vinyl addition polymers of cationic and optionally non-ionic vinyl monomers.
One preferred class is the quatemary ammonia compounds. These quatemary ammonia polymers are generally derived from ethylenically unsaturated monomers containing a quaternary ammonium group or obtained by reaction between an epihalohydrin and one or more amines such as those obtained by reaction between a polyalkylene polyamine and epichlorohydrin or by reaction between epichlorohydrin, dimethyl amine and either ethylenediamine or polyalkylene polyamine.
Cationic polymers are disclosed in U.S. Pat. No. 5,368,694 the disclosure of which is incorporated herein by reference. Generally with all these the molecular weight must be such that the polymer is water soluble or dispersible.
Other suitable cationic polymers include cationized polyacrylamides including polyacrylamides cationized with dimethylsulfate or methyl chloride by the Mannich reactions to varying degrees to achieve varying degrees of cationicity, polymers derived from quatemized dimethyl aminoethylacrylate, dicyanamide-formaldehyde condensates using one or both of formic acid and ammonium chloride as reactants, cationic cellulose starch compounds, carboxylated starch, xanthan gum, guar gum and polyacryllic acid. One preferred cationic polymer is poly-diallyidimethylammonium chloride.
A wide variety of non-ionic surfactants can be used in the present invention. These include ethoxylated fatty alcohols which are either linear or branched and which may have a carbon chain length of anywhere from 8 to 22 carbons. The degree of ethoxylation may vary from 2 moles to 30 moles of ethylene oxide per mole of alcohol. Ethoxylated adducts of octyl phenols as well as ethoxylated polyhydric alcohols including sorbitols or sorbitan esters may be used. Additional non-ionic surfactants include polyethylene oxide/polypropylene oxide block copolymers which would include the Pluronic(copyright) line of surfactants as well as ethoxylated versions of fatty acids and polyethylene glycol esters of phosphates, polyethylene glycol esters of fatty acids including esters derived from one mole of polyethylene glycol and one or two moles of fatty acids, tristyrylphenol ethoxylates and alkylpolyglycosides.
Generally the HLB of these surfactants will be from 7 to 18 with a preferred range being from about 11-13.
The third component of the present invention is an anionic surfactant. Suitable anionic surfactants include water soluble or water dispersible alkylarylsulfonates, sulfonated amines and amides, carboxylated alcohol ethoxylates, diphenylsulfonate derivatives, lignin and lignin derivatives, phosphate esters, soaps of process rosin, sulfates and sulfonates of ethoxylated alkyl phenols, sulfates of ethoxylated alcohol, sulfonates of napthalene and alkylnapthalene, polyethoxy carboxylic acid alcohols from the Neodox(trademark) or Sandopan(trademark) line of products, alky ether sulfates, alkyl benzene sulfonates (branched or linear), alkyl phosphates, alkyl sulfates, alpha olefin sulfonates, diphenyloxide disulfonates sulfosucinnates, ethoxylated sulfosucinnates and succinamates. The preferred surfactant of the present invention is a carboxylic acid capped ethoxylated tridecyl alcohol.
Preferably the composition comprises polydiallyldimethylamoniumchloride in combination with trideceth (7) carboxylic acid and linear alcohol ethoxylate such as Rexonic(copyright) N23-6.5 or Neodol(copyright) N23-6.5.
The amount of anionic surfactant to cationic polymer should be established so that the cationic polymer retains a significant portion of its cationic charge. Generally from 10%-80% of its positive charge should be maintained after the addition of the anionic surfactant.
With only the above three components, the composition will be very acidic. The pH of the composition can be raised by the addition of water soluble bases such as sodium or potassium hydroxide, sodium or potassium carbonate, ammonia, organic amines such as triethanolamine, diethanolamine, monoethanolamine, or morpholine as well as other compatible bases. Sufficient base can be added to establish a desired pH of from about 3 up to about 10 depending on preference for the particular papermaking operation.
The composition of the present invention will generally include 2% to 20% by weight cationic polymer, 2% to 40% by weight nonionic surfactant, 0.5% to 10% anionic surfactant 0% to 5% base with the remainder water.
One preferred formulation is as follows:
with the remainder water.
Preferably the papermaking rolls will be cleaned prior to the initiation of the treatment. This formulation is sprayed directly onto the papermaking rolls as they are moving to maintain the surface of the roller moist with the release formulation. Generally the amount of the composition of the present invention applied to a roll will be about 0.1 to 5 ml/minute for each 10 inches of machine width. This treatment is continued as the papermaking process continues.
The present invention will be further appreciated in light of the following example.